1. Technical Field
The present invention relates to an electrophotographic image forming apparatus, and in particular, to a method and device for preventing the formation of a background image in the electrophotographic image forming apparatus.
2. Related Art
In general, an electrophotographic process is widely employed for an image forming apparatus such as a copier, a laser beam printer (LBP), an LPH (LED Print Head) printer, and a facsimile using plain paper. Such an electrophotographic process consists of the successive steps of charging.fwdarw.exposing.fwdarw.developing.fwdarw.transferring.fwdarw.fixi ng.
Typically, an electrophotographic image forming apparatus employs a contact charging technique by means of which a conductive roller or brush contacts a photosensitive drum to form a uniform electric potential on the surface of the drum. Moreover, the electrophotographic process typically involves a charging step, an exposing step, a developing step, a transferring step, and a fixing step.
Prior electrophotographic image forming apparatus and techniques are burdened by disadvantages. For example, the photosensitive drum has a dark attenuation characteristics; that is to say, with the lapse of time the surface potential of the charged photosensitive drum approaches, for example, 0V! even though it is not exposed to light. Such a phenomena frequently occurs when the apparatus is powered on after a long time in the power-off state, or where the apparatus is powered on and left on for many hours without forming an image.
Therefore, there is a need for the development of a method and device for preventing the formation of a background image in an image forming apparatus, even in the case where the apparatus is powered on after a long time in the power-off state, or where the apparatus is powered on for many hours without forming an image.
The following patents are considered to be representative of the prior art, and are burdened by the disadvantages set forth herein: U.S. Pat. No. 5,500,720 to Karasawa, entitled Bias Application Control Device For Image Forming Apparatus Using Reverse Development, U.S. Pat. No. 5,339,141 to Suzuki et al., entitled Developing Device With A Developer Carrier Capable Of Forming Numerous Microfields Thereon, U.S. Pat. No. 5,309,207 to Omori, entitled Apparatus For Forming Image, U.S. Pat. No. 4,448,867 to Ohkubo et al., entitled Image Forming Method And Device For Same, U.S. Pat. No. 4,674,860 to Tokunagaet al., entitled Image Transfer Device, U.S. Pat. No. 4,444,864 to Takahashi, entitled Method For Effecting Development By Applying An Electric Field Of Bias, U.S. Pat. No. 4,330,199 to Komori et al., entitled Electrophotographic Device, U.S. Pat. No. 3,918,971 to Zweig, entitled Method For Creating Multiple Electrostatic Copies By Persistent Conductivity, U.S. Pat. No. 3,909,258 to Kotz, entitled Electrographic Development Process, U.S. Pat. No. 4,954,843 to Oka et al., entitled Electrophotographic Image Forming Apparatus, U.S. Pat. No. 4,870,460 to Harada et al., entitled Method Of Controlling Surface Potential Of Photoconductive Element, U.S. Pat. No. 3,722,992 to Zweig, entitled Apparatus For Creating An Electrostatic Latent Image By Charge Modulation, and U.S. Pat. No. 5,708,942 to Sugiyama et al., entitled Developing Device For An Image Forming Apparatus.